1. Field of the Invention
The present invention relates to an image forming apparatus including a sensor that detects an object to be detected.
2. Description of the Related Art
A known image forming apparatus using an electrographic process or the like reads a reference image on an image conveyance member using a sensor as a detecting unit, calculates the amount of misalignment from the reference in the result of the reading, corrects the amount of color misalignment and the density of the image, and maintains its proper setting. In this case, the sensor is an optical sensor. Examples of the image conveyance member may include a photosensitive member, an intermediate transfer member, and a transfer material carrier.
For example, in a tandem image forming apparatus employing an intermediate transfer method, a reference image for color misalignment correction for each color is formed on an intermediate transfer member by an image forming portion for each color, the position of the reference image for each color is detected by a sensor, and color misalignment is corrected. In this image forming apparatus, a reference image for density correction for each color is formed on the intermediate transfer member by the image forming portion for each color, the density of the reference image for each color is detected by the sensor, and the density for each color is corrected.
One factor in decreasing the accuracy of detection of the above-described sensor may be a flutter of the reference image, which is an object to be detected. For example, when the intermediate transfer member having an endless belt shape flutters in the direction of the depth of the sensor, there are variations in results of detection of reference images. To avoid such variations, fluttering of the intermediate transfer member may be reduced by arrangement of a roller in a location opposed to the sensor on the inner circumferential surface side of the intermediate transfer member. However, while an image transferred to the surface of the intermediate transfer member (output image or reference image) is passing through a location above the roller having a potential difference therefrom, toner may scatter from the surface of the intermediate transfer member. The scattered toner may be directed toward the detecting surface of the sensor arranged in the vicinity of the intermediate transfer member and may adhere to the detecting surface of the sensor.
An openable and closable shutter member (protective member) for protecting the sensor may be disposed between the sensor and the intermediate transfer member, as described in Japanese Patent No. 4724288.